1. Field of the Invention
The present invention is generally in the field of semiconductor circuits. More particularly, the present invention relates to low leakage semiconductor circuits.
2. Background Art
A conventional flip flop is a memory storage device that typically retains data as long as it is powered on (or “turned on”). While merely retaining data during power on, and not in active use, the flip flop still consumes unnecessary power due to leakage current of the transistors used in the flip flop. When completely powered off, i.e. with the supply voltage being turned off, the conventional flip flop has no leakage current, but also loses stored data.
Flip flops fabricated with transistors having higher threshold voltages and using a lower supply voltage generally have lower leakage currents. However, using higher threshold voltage transistors and a lower supply voltage also results in a reduced operational speed during active use of the flip flops. Conversely, flip flops fabricated with transistors having lower threshold voltages and using a higher supply voltage generally have higher leakage currents. However, using lower threshold voltage transistors and a higher supply voltage results in an increased operational speed during active use of the flip flops.
In an application using conventional flip flops in which power consumption is a design factor, such as in a low power mobile application, flip flop power consumption due to leakage current can be reduced in conventional ways. The threshold voltages of the flip flop transistors can be increased, resulting in power savings at the cost of reduced speed. Alternately, flip flops can be turned off when not in active use, resulting in power savings at the cost of lost data. In this alternative, turning the flip flops back on may involve reading data back into the flip flops from a nonvolatile source, resulting in system and circuit complexity and lost time. In both alternatives, the use of conventional flip flops in the low power mobile application results in various disadvantages such as, for example, increased power consumption, increased complexity and cost, and/or reduced performance.
Thus, there is a need in the art for a low leakage data retention flip flop that overcomes disadvantages of conventional flip flops.